I don't know? It almost looks like a triple punched mint mark. I know that it is not the 1942 D over horizontal D tho. EDIT: I am looking for more info at this time.
My gut reaction is no but I know very little about Jefferson RPM's. What I DO know is that some MDD Mintmarks "look" like RPM's but they are merely isolated MDD. The mintmark you are seeing appears to be in a "pit" if you will. Remembering that what is incused in the coin is in relief on the die. This tells me that there was a build up of metal around the mintmark on the die. That build up "could" have been due to either an aggressive die man at the mint or multiple punches with the hammer. Again, I do not know for sure.
It's a TYPICALL RPM, 3 times o, maybe more. Some presses make sounds like machingun when this happen.
Definitely worthy to submit to Coneca, maybe they'll attribute it for you and credit you with the new find. New varieties are discovered all the time.